I'm going to say Mel was in that campsite and had a really confused idea of what was going on at the time. There was just screaming, and people running, and it was pretty scary. Her dad sent Mel and Ruby to the woods but stayed behind himself - although more from his journalistic curiosity than his Gryffindor courage. They all saw the Dark Mark in the sky and were pretty freaked.
Barney was in a different campsite but saw the mark and immediately started worrying about everyone he knows. He may even have shut up for five minutes.
Lee was also in a different campsite and is somewhat disappointed he didn't get a closer view. However, he probably knows more about what went on than most as Fred and George would have told him everything that Arthur and Ron told them, however much that is. I'm thinking probably not much, but enough.